An electric generator device utilizing electrostatic induction by electret materials has been proposed.
Patent Document 1 proposes an electric generator device wherein an immovable substrate having a plurality of electret electrodes on its surface, and a movable substrate having a plurality of movable electrodes on its surface, are disposed with a space between them.
The movable electrodes and the movable substrate are connected, via an elastic member such as a spring power driver, to a fixed structure provided on the immovable substrate. The movable substrate is constructed to be moved when an external vibration is applied to the electric generator device. It is said to be desirable to utilize environmental vibration, as the external vibration to excite the electric generator device, considering the improvement of power generation efficiency.
The movable substrate is moved by the input of external vibration. Thus, the overlapping area of the electret electrodes and the movable electrodes increases or decreases from the initial area. By this change in the overlapping area, a change in electric charge occurs in the movable electrodes (collecting electrodes). The electric generator device converts an alternating current generated by the change in electric charge, for example, via a converter circuit such as a half-wave rectifier circuit, to a direct current and takes it out as an electric energy, thus accomplishing power generation. In general, the conversion efficiency for converting an alternating current to a direct current by a converter circuit, is known to be better when the frequency and period of the alternating current are constant, than when the frequency and period of the alternating current are irregular.